This invention relates generally to flexible seals and seal assemblies of the type employed in rolling mills where roll necks are journalled for rotation in oil film bearings.
U.S. Pat. No. 2,868,574 discloses one well known example of a prior art seal and seal assembly which has been employed extensively and with considerable success in the rolling mill field. In this arrangement, a flexible seal is mounted on the tapered section of the roll neck for rotation therewith. The seal is surrounded by a stationary circular seal end plate having a radially inwardly extending rigid flange separating oppositely arranged shoulders. The flexible seal has radially outwardly extending flexible flanges which are in sliding contact with inclined shoulder surfaces on the seal end plate. The flange/shoulder surface interface on the bearing side serves to retain bearing lubricant in the bearing, and the flange/shoulder surface interface on the roll side serves to exclude contaminants such as cooling water, mill scale, etc. from penetrating into the bearing.
The above-described arrangement has been in large measure effective as evidenced by its widespread commercial use. Still, problems have been experienced with regard to leakage of bearing lubricant, contamination of bearings and excessive wear of seal components. It has now been determined that these problems are occasioned primarily by the design of the flexible seal flanges, and the manner in which they slidingly engage the surrounding shoulder surfaces of the seal end plate. More particularly, in this prior art construction, the flexible seal flanges are relatively thick and heavy throughout their entire radial length. When the seal is installed, these flanges are bent or flared in opposite directions by the surrounding shoulders of the seal end plate. This creates a heavy pressure at the flange/shoulder friction interface which in turn can result in excessive friction and heat being generated during operation of the mill. The excessive friction accelerates wear of both the flexible flanges and the shoulder surfaces of the seal end plate. The excessive heat has an added adverse effect on the flexible flanges, causing the flange ends to harden and crack. When the flexible flanges become worn, hardened or cracked, the flexible seal must be replaced. Likewise, when the shoulder surfaces on the seal end plate become worn, they must either be reground or if this is no longer possible, the entire seal end plate must be replaced. Such replacements and repairs are both time consuming and expensive. Moreover, any leakage occuring prior to replacement or repair of seal components can result in loss or contamination of bearing lubricant. The foregoing problems, particularly those related to cracking and hardening of the flange ends, have gradually become more severe as rolling speeds have increased.
It has also been determined that the relatively thick heavy flanges of the prior art seal are not as flexible as they should be, and that after being installed, they have a tendency to become permanently distorted (a condition referred to as "taking a set"). This loss of resiliency can have a further adverse effect on sealing integrity.
The oppositely inclined shoulder surfaces on the seal end plate shoulders also present problems, particularly when the roll undergoes axial shifting, a normal occurrency during a rolling operation. When this occurs, the flexible seal flanges will ride along the surrounding shoulder surfaces, thus changing the degree to which the flanges are deflected radially inwardly or outwardly. This changes the pressure at the flange/shoulder surface interface. At one extreme, when a flexible flange undergoes maximum inward deflection, the pressure at the flange/shoulder surface interface is increased and this in turn increases heat and friction. At the opposite extreme, when the flexible flange undergoes maximum outward deflection, the pressure at the flange/shoulder surface interface is decreased, thus raising the possibility that sealing integrity may be lost, particularly when the flexible flange and/or the surrounding shoulder surface has already undergone some frictional wear.
An object of the present invention is the provision of an improved flexible seal of the type generally described above having a novel and improved design which either obviates or at least substantially minimizes the aforementioned problems. In the preferred embodiment to be hereinafter described in greater detail, this is accomplished by providing an angularly disposed flexible lip integrally joined to the outer edge of one or both of the flexible seal flanges. Each lip is preferably joined to its respective flange by a means which accommodates resilient flexure of the lip. Each lip is preferably provided with a gradually diminishing thickness, with its minimum thickness being at the outer lip edge, and with its maximum thickness being less than thickness of the seal flange to which it is integrally joined. With this arrangement, when the seal is mounted on the roll neck within the confines of the seal end plate, each lip is flexed radially inwardly by the surrounding shoulder surface on the seal end plate. Because the lips are capable of being resiliently flexed in relation to their supporting flanges, and because the lips are relatively thin and tapered, and thus relatively more resilient than the flanges, the resulting pressure at the lip/shoulder surface interface is relatively light as compared with the prior art arrangement. By thus reducing the pressure at the lip/shoulder surface interface, friction is reduced, thereby providing longer seal life with improved sealing integrity.
The angular relationship of the lips to their respective flanges is also seen as a decided advantage because centrifugal force will be employed more effectively to urge the lips radially outwardly against the shoulder surfaces of the seal end plate. This effect will increase or decrease in direct proportion to the rotational speed of the roll, thus providing peak pressure at high rolling speeds, when it is most needed, because at higher rolling speeds more oil is pumped through the bearing.
Another objective of the present invention is the provision of an improved seal assembly embodying a flexible seal as described above in combination with a redesigned seal end plate having shoulders which have shoulder surfaces parallel to the rotational axis of the roll neck. With this arrangement, as the roll undergoes axial shifting, the seal lips will not experience changes in radial deflection. Thus, the pressure at the lip/shoulder surface interface will remain unaffected by axial roll shifting, and this in turn will promote longer seal life while reducing wear of the seal end plate shoulders.
Another object of the present invention is the provision of a flexible seal which is better adapted for mounting on the tapered section of a roll neck. In this connection it has been noted that with the prior art seal arrangement, the seal flanges are equal in length when the seal is unmounted. However, the stresses and resulting distortions experienced by the seal body when it is mounted on the tapered section of the roll neck cause the seal flanges to assume different radial lengths in the mounted condition. This problem has now been overcome with the present invention whereby preferably the seal flanges are molded with unequal lengths to compensate for any subsequent seal distortion during mounting.